1. Field of the Invention
The present invention relates to a speed sensor assembly for drive axles. In particular, the present invention relates to a speed sensor assembly mounted to the differential head portion of a drive axle housing for sensing the rotational speed of the driven ring gear and of one of the differential side gears. More particularly, the present invention relates to a dual speed sensor pickup assembly for a speed sensor assembly of the general type described above which is assembled to and removed from the drive axle assembly as a unitary preassembled subassembly.
2. Description of the Prior Art
ABS or anti-lock brake systems are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,604,760; 3,719,841; 3,767,270; 3,854,556; 3,995,912; 3,929,382 and 3,929,383, the disclosures of all of which are hereby incorporated by reference. Briefly, these systems utilize speed sensors, usually a separate sensor assembly at each of the axle ends of each monitored vehicle axle, to sense individual or average rotational wheel speed and to provide signals indicative thereof. Logic means are utilized to receive and process the signals in accordance with predetermined logic rules to determine if an impending or actual wheel-lock condition exists and to issue command output signals to modify the braking force applied to monitored and/or controlled brake sites.
Simplifying such systems by utilizing a single sensor mounted in a relatively protected location within the drive axle housing for sensing the rotational speed of the differential gearing which will provide an average wheel speed signal, is also known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,719,841 and 4,724,935, the disclosures of which are incorporated by reference.
The use of an in-axle wheel speed sensor assembly mounted in the drive axle housing adjacent the differential gearing for sensing an average wheel speed value and an individual wheel speed value (from which both wheel speed values may be calculated) is known in the prior art as may be seen by reference to U.S. Pat. No. 3,769,533, the disclosure of which is incorporated by reference.
While the prior art in-axle speed sensor assemblies are improvements over sensor assemblies mounted at the wheel ends as the sensors and exciters are located at a more protected location and the signals are required to travel a shorter distance and thus be less subject to damage and/or electromagnetic interference, such assemblies were not totally satisfactory as only an average wheel speed was sensed, mounting of the exciter rotors to the gearing required considerable time and/or modification of the existing gearing and/or cross-talk interference between two closely spaced sensor pickups was not minimized.